The present invention relates to a method and apparatus for ejecting target mass. In particular, but not exclusively, the present invention provides a method and apparatus for a fast mass ejection device able to eject liquid and/or liquid vapour quickly and over relatively long distances from an ejection chamber in which a quantity of liquid is stored. The present invention also relates to the many uses of such an ejection system. Still more particularly, but again not exclusively, the present invention relates to an inhaler and/or nebulizer and/or needleless injector which are able to deliver drugs to a user.
There is a need in a number of industries for mass ejection devices. That is to say, devices which will send out a spray of liquid and liquid vapour at a fixed or variable rate and over a desired distance. Preferably there is a need for a spray of liquid and liquid vapour to occur at a fast rate and over a great distance. In such systems the term “throw” is often referred to as a characteristic of a spray. The throw of material is defined as the distance travelled divided by the length of a chamber from which the spray is ejected.
Various examples of mass ejection devices are known such as fire extinguishers, ink jet printers, air bag igniters, fuel injectors for motor engines and gas turbines, respiratory drug delivery systems, etc. In each of these there are specific problems associated with the device in question, however, for each applied technology there is a continuing desire to be able to eject liquid and liquid vapour quickly and over a large distance.
By way of example of a problem specific to an application of mass ejection systems, reference is made to a gas turbine reigniter. In the igniter of a gas turbine, the conventional approach to reignite gas in a combustion chamber is to pass a current between two electrodes of a reigniter and create for a short while a mixture of electrically charged radicals. This is illustrated more clearly in FIG. 1 in which a conventional reigniter 10 is shown including an outer electrode 11 which is generally cylindrical in shape with an internally located pellet 12. A central electrode 13 is located within the pellet and by passing a current between the two electrodes 11, 13 a mixture of electrically charged radicals (that is when the gas molecules split temporarily into charged components referred to as a plasma). This plasma only lasts for a fraction of a second before recombining and losing its charge. The charge is then used to ignite combustion in a main combustion chamber of the main engine. A problem with such known reigniters is in getting the mixture to be ejected as ejected material via the exit orifice 14 far enough and to remain charged long enough to perform its objective function. The ejected material 15 has been used to ignite the kerosene or other usual gas turbine engine fuel.
By way of a further example of a problem specific to an application of mass ejection systems, reference is made to respiratory drug delivery systems. Respiratory drug delivery systems are used to deliver drugs directly to the respiratory system to treat respiratory diseases such as asthma, cystic fibrosis, chronic obstructive pulmonary disease (COPD) and others. Additionally, in recent times it has been realised that the lungs can be used as a portal of entry for systematic drug therapy, for example inhaled insulin has been successfully administered and is likely to become an alternative routine treatment to injecting insulin in the therapy of diabetes.
There are currently three main types of respiratory drug delivery systems. These are metered dose inhalers, dry powder inhalers and nebulizers. Pressurized metered dose inhalers release a metered volume of pressurised fluid into a patient's airways, on release the fluid evaporates rapidly leaving the drug in dry form suitable for inhalation. Dry powder inhalers contain a dry powder which is dislodged when the patient inhales air through the inhaler, the force of the patient's inhalation then carries the dry powder into the lungs of the patient. Both metered dose inhalers and dry powder inhalers will give out a predetermined amount of drug in one inhalation, the patient will take a certain amount of these doses during a day. A third type of respiratory drug delivery system is the nebulizer which converts medicine stored in liquid form into a gaseous suspension of medicine particles, known as an aerosol or mist. The patient will breathe in this mist and the drug is delivered into the respiratory system. There are two main types of nebulizer, jet nebulisers and ultrasonic nebulizers. Jet nebulizers work by applying pressurised gas through a narrow opening which creates a negative pressure upon a medicine reservoir, drawing particles of the drug solution from its reservoir forming a mist for the patient to inhale. Ultrasonic nebulizers can use a rapidly vibrating piezoelectric crystal which forms a fountain of liquid from which the mist arises. Nebulizers slowly convert the medicine reservoir into a mist over a period of about 15 minutes, during which time the user will be continually inhaling the medicine in mist form. Nebulizers can deliver much stronger doses of medicine than other types of drug delivery methodologies and are therefore often used for patients with severe respiratory problems.
A major problem with known respiratory drug delivery systems is that of ensuring that the drug is inhaled fully into the respiratory system so that the medicine gets to where it is meant to. Respiratory drug delivery systems need to maximise the throw and dispersion of the drug when ejecting active ingredients. A further problem is that when the medicine is particulated or atomised, the medicine particles may be too large and are then likely to be deposited within the oral cavity. If too small, it is likely the active ingredients will not be deposited and will be exhaled by the patient.